What is the primary mechanism through which allopatric speciation occurs?

Allopatric speciation occurs primarily through geographic barriers that lead to the isolation of populations. When a population becomes divided by a physical barrier, such as a mountain range, river, or ocean, the separated groups can no longer interbreed. This isolation prevents gene flow between the populations and allows them to evolve independently. Over time, genetic divergence can occur due to different selective pressures, mutations, and adaptations to their respective environments, potentially leading to the emergence of new species.

In this context, geographic barriers are crucial as they initiate the process of allopatric speciation by stopping the exchange of genetic material, which is essential for the evolution of distinct species. Other mechanisms, while significant in other forms of speciation, do not specifically define allopatric speciation. Thus, the role of geographic isolation is fundamental to this process.